Looks to me like you were feared through the ground... my guess would be Blizzard made a mechanic that throws you high enough in the air to kill you if you go below the ground. I recall something in the past about people exploiting / using hacks to go underground in arenas or bgs, so my best guess would be it's an antihack mechanic.

Originally Posted by Utinil

The Nitro Boost has 2 different malfunctions. One causes you to take 50% of your health in fire damage over a short period of time and the other sends you flying way up in the air.

Whenever you use it you should always be ready to hit your parachute cloak just in case.

A small correction: Rocket Fuel Leak takes 10% of your max hp every second for 8 seconds, so a total of 80% hp. If you are out of combat and low health,you can take off all your gear since you don't stay at whatever % hp you were at, but the absolute value, so after taking off gear, even with low hp, you can get to 100% and you'll survive.

You were horrified underwater (slow), and then you glitched through the landscape. When this happened, you and your mount ran at full speed (non-underwater) in one direction, and that just happened to be that steep incline in the direction of the flag. This speed launched you into the air.